Three-Coordinate NiII: Tracing the Origin of an Unusual, Facile Si−C(sp3) Bond Cleavage in [(tBu2PCH2SiMe2)2N]Ni+

All attempts to synthesize (PNP)Ni(OTf) form instead (tBu2PCH2SiMe2NSiMe2OTf)Ni(CH2PtBu2). Abstraction of F− from (PNP)NiF by even a catalytic amount of BF3 causes rearrangement of the (transient) (PNP)Ni+ to analogous ring-opened [(tBu2PCH2SiMe2NSiMe2F)]Ni(CH2PtBu2). Abstraction of Cl− from (PNP)NiCl with NaB(C6H3(CF3)2)4 in CH2Cl2 or C6H5F gives (PNP)NiB(C6H3(CF3)2)4, the key intermediate in these reactions is (PNP)Ni+, [(PNP)Ni]+, in which one Si−C bond (together with N and two P) donates to Ni. This makes this Si−C bond subject to nucleophilic attack by F−, triflate, and alkoxide/ether (from THF). This σSi−C complex binds CO in the time of mixing and also binds chloride, both at nickel. Evidence is offered of a “self-healing” process, where the broken Si−C bond can be reformed in an equilibrium process. (PNP)Ni+ reacts rapidly with H2 to give (PN(H)P)NiH+, which can be deprotonated to form (PNP)NiH. A variety of nucleophilic attacks (and THF polymerization) on the coordinated Si−C bond are envisioned to occur perpendicular to the Si−C bond, based on the character of the LUMO of (PNP)Ni+.